1. Field of the Invention
The present invention concerns measurements of viscosity and related fluid properties. It finds particular application in uses of sensors that employ reciprocating magnetically driven bobs.
2. Background Information
Fluids' rheological characteristics have been subjects of study for well over a century, and measurements have for nearly as long been made in laboratories routinely to characterize fluids that have been newly developed or encountered. Instruments used for this purpose usually employ some rotated cylindrical member to subject the fluid of interest to shearing, and various rheological properties are inferred from the fluid's resistance to such shearing at various cylinder speeds. Examples of the characteristics that such instruments determine are whether the fluid is Newtonian, what its shear sensitivity is, what its relationship is between shear stress and shear rate, what its yield stress is, and whether it is complex in the sense that its viscosity drifts with extended exposure to shearing.
Such methods of rheological-characteristic determination have proved quite effective and accurate, but there are a range of applications in which they have not proved very practical. Some research, for example, involves screening large numbers of fluids that are expensive to formulate. The expense of some such fluids has tended to dissuade researchers from screening them.